The U.S. Supreme Court on Friday agreed to decide whether states can ban gay marriage, delving into a contentious social issue in what will be one of the most anticipated rulings of the year.

The court, in a brief order, said it would hear cases concerning marriage restrictions in Michigan, Kentucky, Ohio and Tennessee. The ruling, due by the end of June, will determine whether 14 remaining state bans will be struck down.

The court said it will decide two questions: Whether states must allows same-sex couples to marry and whether states must recognize same-sex marriages that take place out-of-state. The court will hear an extended two and a half hours of oral arguments.

There has already been a legal sea change on the issue, thanks in large part to the Supreme Court’s prompting. It began in earnest in June 2013 when the court struck down a federal law that restricted, for the purpose of federal benefits, the definition of marriage to heterosexual couples.

Judges around the country later seized on the language in the decision, written by swing vote Justice Anthony Kennedy, to strike down a series of state bans.

At the time of the 2013 ruling, only 12 states had authorized gay marriage. It is now legal in 36 of the 50 states.